Set MSBUILDDEBUGPATH in build scripts for reliable crash diagnostics

[danmoseley]

Set MSBUILDDEBUGPATH directly in eng/build.sh for reliable crash diagnostics

PR #126012 added MSBUILDDEBUGPATH as an AzDO pipeline variable in global-build-job.yml so that MSBuild crash diagnostics (MSBuild_*.failure.txt) would be written to artifacts/log/ instead of the system temp directory. However, recent builds that hit the MSB4166 crash (e.g., build 1370423) still show MSBuild writing to the default temp path, indicating the pipeline variable is not reaching the MSBuild process.

Other build scripts (src/coreclr/build-runtime.sh, src/tests/build.sh) already set and export MSBUILDDEBUGPATH independently, which is why "Build Tests" steps work. The "Build product" step calls eng/build.sh, which did not set it.

This PR sets MSBUILDDEBUGPATH directly in eng/build.sh and eng/build.ps1 before any common/build.sh/common/build.ps1 invocations, matching the pattern used by the other scripts. This also:

• Creates the directory with mkdir -p before MSBuild starts (MSBuild's EnsureDirectoryExists has no try/catch in its static constructor, so a failed directory creation would silently fall back to the temp dir)
• Echoes the path for diagnostic visibility in build logs
• Covers both the bootstrap and product build invocations

The existing pipeline variable in global-build-job.yml is left in place as defense-in-depth.

Relates to getting data to fix #92290

[Copilot]

Pull request overview

This PR ensures MSBuild crash diagnostics (e.g., MSBuild_*.failure.txt from MSB4166) are consistently written under artifacts/log/ by setting up and exporting MSBUILDDEBUGPATH directly in the top-level build scripts (eng/build.sh and eng/build.ps1), rather than relying solely on CI pipeline variables.

Changes:

• Set and export MSBUILDDEBUGPATH in eng/build.sh and create the target directory before invoking MSBuild.
• Set and export MSBUILDDEBUGPATH in eng/build.ps1, create the target directory, and update it per-configuration when building multiple configurations.

Show a summary per file

File	Description
eng/build.sh	Adds MSBUILDDEBUGPATH initialization + mkdir -p so MSBuild crash logs land under artifacts/log/<Config>/MsbuildDebugLogs.
eng/build.ps1	Adds MSBUILDDEBUGPATH initialization + directory creation, and updates the env var per configuration in multi-config builds.

Copilot's findings

Comments suppressed due to low confidence (1)

eng/build.ps1:451

• Same as above: inside the per-configuration loop, New-Item errors are non-terminating by default. If directory creation fails, the build continues and MSBuild crash diagnostics may not be captured under artifacts/log. Make directory creation terminating (e.g., -ErrorAction Stop) to ensure reliability.

  $msbuildDebugLogsDir = "$PSScriptRoot/../artifacts/log/$titleCaseConfig/MsbuildDebugLogs"
  New-Item -ItemType Directory -Force -Path $msbuildDebugLogsDir | Out-Null
  $env:MSBUILDDEBUGPATH = $msbuildDebugLogsDir

• Files reviewed: 2/2 changed files
• Comments generated: 2

[Copilot]

Pull request overview

Updates top-level build entrypoints to ensure MSBuild crash diagnostics (MSBuild_*.failure.txt from MSB4166/node crashes) are consistently written under artifacts/log/ so CI reliably publishes them.

Changes:

• Set and export MSBUILDDEBUGPATH early in eng/build.sh, create the directory, and print it for diagnostics.
• Set and export MSBUILDDEBUGPATH early in eng/build.ps1, create the directory, print it, and update it per configuration during multi-config builds.

Show a summary per file

File	Description
eng/build.sh	Exports MSBUILDDEBUGPATH to a stable artifacts/log/<config>/MsbuildDebugLogs directory before invoking eng/common/build.sh.
eng/build.ps1	Exports MSBUILDDEBUGPATH to artifacts/log/<config>/MsbuildDebugLogs, ensures the directory exists, and adjusts it when iterating configurations.

Copilot's findings

• Files reviewed: 2/2 changed files
• Comments generated: 1

[Copilot]

In the multi-configuration loop you update $env:MSBUILDDEBUGPATH per config, but MSBuild node reuse is enabled by default for non-CI runs (/nr:true via eng/common/tools.ps1 where nodeReuse defaults to !$ci). Reused nodes won’t see the updated environment variable, so crash diagnostics may still be written to the previous configuration’s directory, making the per-config directory update potentially misleading. Consider either keeping a single MSBUILDDEBUGPATH for the whole build.ps1 invocation, or disabling node reuse when switching configurations so each config reliably writes to its intended directory.

See below for a potential fix:

# Use a single MSBuild debug logs directory for the entire invocation because
# reused MSBuild nodes do not observe environment variable updates made between
# configurations.
$msbuildDebugLogsDir = "$PSScriptRoot/../artifacts/log/MsbuildDebugLogs"
New-Item -ItemType Directory -Force -Path $msbuildDebugLogsDir | Out-Null
$env:MSBUILDDEBUGPATH = $msbuildDebugLogsDir
Write-Host "MSBUILDDEBUGPATH=$msbuildDebugLogsDir"

foreach ($config in $configuration) {
  $titleCaseConfig = $((Get-Culture).TextInfo.ToTitleCase($config))